Devising Face Authentication System and Performance Evaluation Based on Statistical Models

The modern world has seen a rapid evolution of the technology of biometric authentication, prompted by an increaing urgency to ensure a system's security. The need for efficient authentication systems has skyrocketed since 9/11, and the proposed inclusion of digitized photos in passports shows the importance of biometrics in homeland security today. Based on a person's essentially unique biological traits, these methods are potentially more reliable than traditional identifiers like PINs and ID cards. This paper focuses on demonstrating the use of statistical models in devising efficient authentication systems today that are capable of handling real-life applications. First, we propose a novel Gaussian Mixture Model-based face authentication approach in the frequency domain by exploiting the well-known significance of phase in face identification and illustrate that our method is superior to the non-model based state-of-the-art system called the Minimum Average Correlation Energy (MACE) filter in terms of performance on a database of 65 people under extreme illumination conditions. We then introduce a general statistical framework for assessing the predictive performance of a biometric system (including watch-list detection) and show that our model-based system outperforms the MACE system in this regard as well. Finally, we demonstrate how this framework can be used to study the watch-list performance of a biometric system.</p

Structural and mechanical properties of folded protein hydrogels with embedded microbubbles

Globular folded proteins are powerful building blocks to create biomaterials with mechanical robustness and inherent biological functionality. Here we explore their potential as advanced drug delivery scaffolds, by embedding microbubbles (MBs) within a photo-activated, chemically cross-linked bovine serum albumin (BSA) protein network. Using a combination of circular dichroism (CD), rheology, small angle neutron scattering (SANS) and microscopy we determine the nanoscale and mesoscale structure and mechanics of this novel multi-composite system. Optical and confocal microscopy confirms the presence of MBs within the protein hydrogel, their reduced diffusion and their effective rupture using ultrasound, a requirement for burst drug release. CD confirms that the inclusion of MBs does not impact the proportion of folded proteins within the cross-linked protein network. Rheological characterisation demonstrates that the mechanics of the BSA hydrogels is reduced in the presence of MBs. Furthermore, SANS reveals that embedding MBs in the protein hydrogel network results in a smaller number of clusters that are larger in size (∼16.6% reduction in number of clusters, 17.4% increase in cluster size). Taken together, we show that MBs can be successfully embedded within a folded protein network and ruptured upon application of ultrasound. The fundamental insight into the impact of embedded MBs in protein scaffolds at the nanoscale and mesoscale is important in the development of future platforms for targeted and controlled drug delivery applications.</p

Encapsulation of Microbubbles within Folded Protein Hydrogels: Effects on the mechanical and structural properties

The data covers a study of folded protein hydrogel with embedded microbubbles, and their examination using rheology, small angle scattering and microscopy

Distinguishing short and long memory volatility specifications

Asset price volatility appears to be more persistent than can be captured by individual, short memory, autoregressive or moving average components. Fractional integration offers a very parsimonious and tempting formulation of this long memory property of volatility but other explanations such as structural models (aggregates of several autoregressive components) are possible. Given the ability of the latter to mimic the former, we investigate the extent to which it is possible to distinguish short from long memory volatility specifications. For a likelihood ratio test in the spectral domain, we investigate size and power characteristics by Monte Carlo simulation. Finally applying the same test to Sterling/Dollar returns, we draw conclusions about the minimum number of structural factors that must be present to mimic the long memory volatility properties that are empirically observed

Malleability of the Folding Mechanism of the Outer Membrane Protein PagP: Parallel Pathways and the Effect of Membrane Elasticity

Understanding the interactions between membrane proteins and the lipid bilayer is key to increasing our ability to predict and tailor the folding mechanism, structure and stability of membrane proteins. Here, we have investigated the effects of changing the membrane composition and the relative concentrations of protein and lipid on the folding mechanism of the bacterial outer membrane protein PagP. The folding pathway, monitored by tryptophan fluorescence, was found to be characterized by a burst phase, representing PagP adsorption to the liposome surface, followed by a time course that reflects the folding and insertion of the protein into the membrane. In 1,2-dilauroyl-sn-glycero-3-phosphocholine (diC12:0PC) liposomes, the post-adsorption time course fits well to a single exponential at high lipid-to-protein ratios (LPRs), but at low LPRs, a second exponential phase with a slower folding rate constant is observed. Interrupted refolding assays demonstrated that the two exponential phases reflect the presence of parallel folding pathways. Partitioning between these pathways was found to be modulated by the elastic properties of the membrane. Folding into mixed 1,2-dilauroyl-sn-glycero-3-phosphoethanolamine:diC12:0PC liposomes resulted in a decrease in PagP adsorption to the liposomes and a switch to the slower folding pathway. By contrast, inclusion of 1,2-dilauroyl-sn-glycero-3-phosphoserine into diC12:0PC liposomes resulted in a decrease in the folding rate of the fast pathway. The results highlight the effect of lipid composition in tailoring the folding mechanism of a membrane protein, revealing that membrane proteins have access to multiple, competing folding routes to a unique native structure

The N-terminal Helix Is a Post-assembly Clamp in the Bacterial Outer Membrane Protein PagP

The Escherichia coli outer membrane β-barrel enzyme PagP and its homologues are unique in that the eight-stranded barrel is tilted by about 25° with respect to the membrane normal and is preceded by a 19-residue amphipathic α-helix. To investigate the role of this helix in the folding and stability of PagP, mutants were generated in which the helix was deleted (Δ(1-19)), or in which residues predicted to be involved in helix–barrel interactions were altered (W17A or R59L). The ability of the variants to insert into detergent micelles or liposomes was studied in vitro using circular dichroism, fluorescence, Fourier transform infrared spectroscopy, electrophoretic mobility and gain of enzyme activity. The data show that PagP, initially unfolded in 5% (w/v) perfluoro-octanoic acid or 6 M guanidinium chloride, inserts spontaneously and folds quantitatively to an active conformation into detergent micelles of cyclofos-7 or into large vesicles of diC12:0-phosphatidylcholine (diC12:0PC), respectively, the latter in the presence of 7 M urea. Successful refolding of all variants into both micelles and liposomes ruled out an essential role for the helix or helix–barrel interactions in folding and membrane insertion. Measurements of thermal stability indicated that the variants R59L, W17A/R59L and Δ(1-19) were destabilised substantially compared with wild-type PagP. However, in contrast to the other variants, destabilisation of the W17A variant relative to wild-type PagP was much greater in liposomes than in micelles. Analysis of the kinetics of folding and unfolding of all variants in diC12:0PC liposomes suggested that this destabilisation arises predominantly from an increased dissociation of the refolded variant proteins from the lipid-inserted state. The data support the view that the helix of PagP is not required for folding and assembly, but instead acts as a clamp, stabilising membrane-inserted PagP after folding and docking with the membrane are complete